This invention relates to controlling the flow of air in a forced-air HVAC system. In particular, this invention offers a means to monitor the system temperature and, in response thereto, to vary continuously the speed of the fan or blower whenever the system operates.
Present forced-air HVAC systems control the speed of a fan or blower motor, generally an induction motor, in one of three ways: (1) the fan runs at full speed, (2) the fan speed is stepped, or (3) the fan cycles on and off when the system operates. In these systems, the flow of forced air is discontinuous. It does not start until well after the system has called for the flow of heated or cooled air. Thus premises with more than one room that are served by a single HVAC system can develop hot and cold air pockets throughout the occupied space. Therefore, for optimal comfort, there is need for a continuous flow of air, circulating at varying velocities, to mix air above and below the thermostatically set level and eliminate pockets at non-optimal temperatures, thereby bringing to a substantially single optimal temperature the entire space to be heated or cooled. Depending on the season, both heating and cooling may be required during a single period to keep the space at the substantially single optimal temperature set by at least one thermostat.
Most forced-air HVAC systems use the air temperature of only one occupied space to cycle the fan or blower on and off. Other systems use the difference between the respective air temperatures in a plenum and in a return to turn the fan or blower on and off, e.g., U.S. Pat. No. 6,684,944 to Byrnes et al. These systems cause a delay in supplying air at an optimal temperature. Still other systems open and close dampers to control temperature in the space to be heated or cooled. In none of these systems of the prior art does the blower/fan motor operate continuously. Thus, to obtain an optimal temperature, there is a need to monitor continuously the heating plenum and/or cooling coil and to adjust accordingly the blower/fan motor speed continuously to overcome the drawbacks of the prior art and keep the space at a substantially single and stable optimal temperature.